The present invention relates to a hydraulic control arrangement in general, and more particularly to an arrangement for controlling the flow of a hydraulic fluid to and from a hydraulic user.
There are already known various arrangements for controlling the flow of a hydraulic fluid between a fluid reservoir, a pump and a user. Such arrangements usually include a control slide which may be elongated and include a plurality of annular control lands and which is longitudinally shiftably received in a bore of a housing which has a plurality of annular chambers surrounding the bore. Then, as the control slide is being shifted longitudinally thereof between a plurality of displaced positions, the various lands establish and interrupt communication between the various chambers of the housing which, in turn, are in communication with various conduits of a hydraulic circuit interconnecting the user, the pump and the fluid reservoir. When it is desired to gradually rather than abruptly control the communication between the various chambers of the housing accommodating the control slide, it is also already known to provide at least one of the lands with a bevelled control edge which, together with the cooperating control edge of the respective chamber, forms a throttling gap the size of which is adjusted in dependence on the extent of displacement of the control slide.
In one of the conventional arrangements of this type which is revealed in the German Pat. DT-PS No. 1,928,896, a main control slide is used for controlling the communication with the fluid reservoir of a pressure throttle which communicates the pump with the user through an input chamber, the main control slide forming an adjustable throttle which influences the operation of a flow-regulating valve which is arranged in parallel to the main control slide between the pump and the fluid reservoir. This conventional control arrangement includes a control conduit which communicates the flow-regulating valve with a switching chamber the communication of which with the fluid reservoir is controlled by the main control slide. The main control slide has an internal compartment which accommodates an auxiliary control slide of movement in the compartment, the auxiliary control slide controlling the communication of the switching chamber with the fluid reservoir in dependence on the position of the main control slide. The pressure channel of this arrangement also passes through the switching chamber. A fine-adjustment bevelled edge on the main control slide serves to control the flow of the hydraulic fluid to the user proportionally to the displacement of the main control slide, the fine-adjustment bevelled edge controlling the communication between the input chamber and the switching chamber which is located adjacent to the input chamber. The pressure differential between the input and the switching chamber is controlled by a slide of the flow-regulating valve. The fine-adjustment bevelled edge is located at a section of the main control slide in which there is additionally provided a compartment which accommodates the auxiliary control slide which acts as a rapidswitching valve.
As a result of this arrangement of the auxiliary control slide within the main control slide, the amount of available space is drastically limited so that it is impossible to provide a passage of an increased flow-through cross-sectional area adjacent to the fine-adjustment region. As a result of the special arrangement of the flow-regulating valve of this reference, this results in a situation in which the user cannot be supplied with substantial amounts of the hydraulic fluid per unit time, in view of the fact that the available flow-through cross-sectional area acts as a throttle and, as a result of this throttling action, the slide of the flow-regulating valve permits some of the fluid being pumped by the pump to return into the fluid reservoir. While it is true that it is possible to increase the flow rate of the hydraulic fluid from the pump to the user by increasing the pre-tension of a spring which acts on the slide of the flow-regulating valve, the resort to this measure results in an undesired increase in the resistance of the flow-regulating valve to the flow of the hydraulic fluid in the neutral position of the main control slide in which the hydraulic fluid is neither delivered to nor discharged from the user. Under these circumstances all of the output of the hydraulic fluid from the pump is being returned to the fluid reservoir through the flow-regulating valve. It will be appreciated that the above-mentioned increase in the resistance of the flow-regulating valve to the flow of the hydraulic fluid therethrough will result in considerable energy losses.
In addition thereto, this conventional control arrangement has the disadvantage that, in order to avoid a malfunction, the switching chamber is protected by arranging an additional checkvalve in the pressure chamber so as to assure that, in the de-energizing position of the main control slide, no pressurized fluid can flow from the user to the flow-regulating valve and influence the operation thereof. Were it otherwise, the flow-regulating valve could become closed at a time when closing of this valve is undesired. However, because of the need for providing the additional check valve, the control arrangement becomes too expensive in terms of manufacturing costs thereof.